In generally utilized inert gases such as nitrogen used in industry, oxygen is contained as an impurity although a total amount thereof is very small. This oxygen impurity induces a certain possibility that oxygen molecules cause a problem in such steps that should avoid oxidation in various fields. For instance, oxygen molecules may cause problems when metal thin films are formed by CVD methods, sputtering methods, and the like; when intermetallic compounds are manufactured; when wiring patterns are processed in semiconductor manufacturing steps, and so on.
As to the gases used in the above-described cases, such gases are utilized from which oxygen molecules have already been removed by employing usual methods such as adsorption or absorption of oxygen, catalytic reaction, and the like. However, in the case that such a low oxygen partial pressure that is lower than the oxygen partial pressure obtained by performing the conventional method is required, for example, in such a case that very easily oxidizable substances are handled, the above-explained usual methods are not good enough and thus gases having extremely low oxygen partial pressure are of absolute necessity.
As one of the means capable of generating such extremely low oxygen partial pressure, an oxygen molecule removing apparatus called an “oxygen pump” with employment of solid electrolytes such as strontium-doped lanthanum gallate is already known. There the solid electrolytes having cylinder structures generate gases having high oxygen partial pressures down to low oxygen partial pressures by controlling operating voltages in a feedback manner based upon oxygen partial pressure values acquired from oxygen sensors (Patent Document 1).
Also, other techniques are known (Patent Document 2 and Patent Document 3), by which low oxygen gases obtained by an oxygen pump are fed back to the pump through a return path, realizing even lower oxygen partial pressures which are lower than 10−21 atm and higher than 10−30 atm.
Also, in semiconductor manufacturing apparatuses and electric/electronic component manufacturing apparatuses, when these manufacturing apparatuses are vacuum-exhausted from the atmospheric pressure, the below-mentioned method has been employed to realize vacuum conditions having superior qualities without moisture: That is, the manufacturing apparatuses are heated to temperatures from 100° C. to 200° C. while being evacuated so as to heat-remove water content adhered onto wall portions within these manufacturing apparatuses, which are made of stainless steel, aluminum, or the like, to improve the ultimate vacuum. Also, when semiconductor devices and electric/electronic components are manufactured, the below-mentioned method has been employed: That is, performing a thin film deposition process, a heat treatment process, and an etching process in apparatuses where the ultimate vacuum is sufficiently good to make residual water content in semiconductor thin films as low as possible. As a result, degradation of the film, oxidation thereof, and deteriorations of reliability which are caused by water can be avoided. Also, an additional treatment is normally carried out, namely, after the thin film has been deposited, water is heat-removed from the deposited thin film. Moreover, various sorts of structural components which constitute the semiconductor or electric/electronic component manufacturing apparatuses are heat-treated within vacuum baths for sufficient dehydration prior to assembling.
[Patent Document 1] JP-T-10-500450
[Patent Document 2] JP-A-2002-326887
[Patent Document 3] JP-A-2005-331339